imperishable vs unkillable

imperishable

adj
  • not perishable; not subject to decay; enduring permanently 

noun
  • something that does not perish, or keeps for a long time 

unkillable

adj
  • Not killable; unable to be killed. 

How often have the words imperishable and unkillable occurred in a corpus of books? (source: Google Ngram Viewer )